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[174.21.143.238]) by smtp.gmail.com with ESMTPSA id p10sm3783746pgn.6.2020.07.02.10.37.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jul 2020 10:37:29 -0700 (PDT) Subject: Re: [PATCH 0/6] target/riscv: NaN-boxing for multiple precison To: LIU Zhiwei , qemu-devel@nongnu.org, qemu-riscv@nongnu.org References: <20200626205917.4545-1-zhiwei_liu@c-sky.com> From: Richard Henderson Message-ID: <6d2e6876-18a8-b32a-0879-565693b6d446@linaro.org> Date: Thu, 2 Jul 2020 10:37:27 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200626205917.4545-1-zhiwei_liu@c-sky.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::544; envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x544.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: palmer@dabbelt.com, wenmeng_zhang@c-sky.com, Alistair.Francis@wdc.com, ianjiang.ict@gmail.com, wxy194768@alibaba-inc.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/26/20 1:59 PM, LIU Zhiwei wrote: > Multiple precison shoule be supported by NaN-boxing. That means, we should > flush not valid NaN-boxing input to canonical NaN before effective > calculation and we should NaN-boxing the result after the effective > calculation. > > In this patch set, split the implementation to three steps for compute, > sign-injection, and some covert insns, which are check_nanboxed, > effective calculation and gen_nanbox_fpr. > > Check_nanboxed checks the inputs and flushes not valid inputs to cancical NaN. > Effective calculation is direct calculation on fp32 values. > Gen_nanbox_fpr does the NaN-boxing, writing the 1s to upper 32 bits. I know I just reviewed a couple of these, but then I got to thinking about patch 3 more closely. I think it would be better to do all of the nan-boxing work inside of the helpers, including the return values. Since we must have a helper call for the actual fp arithmetic, we might as well put the rest of the logic in there too. That way the JIT code is smaller. If, for RVF && !RVD, we always maintain the invariant that the values are nanboxed anyway, then we do not even have to check for RVD at runtime. Thoughts? r~